Microwave asher assemblies for the manufacture of semiconductor devices are typically manufactured with waveguides designed to resonate microwaves to ignite a plasma source for semiconductor ashing. To ensure that the waveguide length is appropriate for a power setting, ashers may be equipped with a tuning slug at one end of the waveguide. This tuning slug allows an operator to somewhat control the length of the waveguide, thus reducing the amount of reflected power within the waveguide to increase ensuring maximum efficiency of the energy used to excite the plasma.
Adjustment of the tuning slug typically is performed by a set screw assembly that must be adjusted by hand in a way that is cumbersome, imprecise, and in some cases dangerous. Generally, a stem of the tuning slug is inserted through an opening in the end of the waveguide and is secured by a set screw through the opening to lock the tuning slug into position. When a changed waveguide length is desired, for example due to a change in the power setting, an operator must loosen the set screw and adjust the tuning slug either by hand, by tapping with a hammer, or by some other imprecise means. Typically, after each adjustment, an operator must turn on the power of the waveguide assembly, check the reflected and transmitted power measurements of the waveguide, turn off the microwave generator of the asher and readjust the tuning slug based on the previous readings of power reflection in transmission. This process is then repeated until a certain level of reflected power is achieved. This method of adjusting the tuning slug often results in a large amount of microwave energy escaping the waveguide, which presents health concerns to individuals, particularly those with pacemakers or other devices sensitive to microwave radiation. Furthermore, repeated loosening and tightening of the set screw against the stem of the tuning slug causes damage to the tuning slug and may result in costly replacement of the slug.